1. Field of the Invention
The present invention relates to oil scraper piston rings for internal combustion engines, and more particularly to compound oil scraper piston rings having corrugated radial spacer expander.
2. Description of the Prior Art
Compound oil scraper piston rings consisting of a corrugated spacer expander and two side rails have been preferred for use in modern high power and high speed internal combustion engines, because of their high contact pressure against the cylinder wall and good following character with respect to the cylinder wall. In addition, those compound oil scraper piston rings can conveniently prevent a pumping action since they can provide sealing at both their upper and lower surfaces.
A conventional compound oil scraper piston ring comprises a corrugated radial spacer expander which has a corrugation in the circumferential direction thereof. The corrugation consists of alternating valleys and crests connected by flanks interposed therebetween. This corrugated radial spacer expander is adapted for use in combination with two side rails which are meant to engate the cylinder wall to scrape the oil down and to keep the required gas tightness, which engagement is ensured by radial expansion force exerted by the spacer expander.
When the compound oil scraper piston ring is mounted on a piston, the spacer expander is opened at its opposing ends and is fitted into the peripheral groove in the piston, and then the two side rails are fitted.
It is inconvenient that, during this fitting of two side rails, the two opposing ends of the spacer expander are likely to overlay one on the other, i.e. the lower side of the valley of one end is caught by the upper side of the valley of the other end.
Unfortunately, there have been no means to make one become aware of this extraordinary overlapping before the piston is inserted into the cylinder.
It is clear that this overlapping renders the compound oil scraper ring in operative, because of the poor expansion force exterted by the spacer expander, resulting in increased lubricating oil consumption which may lead to an unexpected engine stalling.